Where exactly is my tach wire?

[User_name]

I've been searching. Camt find exactly what I'm looking for.
I'm still having the intermittent fluttering tachometer and miss EVERY TIME THE TACH FLUTTERS.
Things I've ruled out:
11-12 psi fuel pressure constantly
New delphi dizzy (including ignition module)
Wiring harness looks ok..
Grounds are good.
Timing is at 0* (unless my balancer has slipped)

So which wire on the coil or distributor is the tach wire? I want to disconnect the tachometer. I was talking with an old gear head and he said that he's seen this happen on the old big cap hei systems because the tach it's self has a short. This is the last straw with this thing for me...
1995 chevy c2500 5.7 tbi nv4500 tranny.

 

[DerekTheGreat]

Old school HEI isn't the same as TBI HEI.

If it's missing every time you see flutter, disconnecting the wire to the tach won't solve the issue. Not sure about a '95, but I'm confident that there are two tach signal wires, one for the ECM and one for the cluster. They're both driven by the ICM and the ECM needs to see that signal to properly meter out fuel so you can't disconnect it.

The tach is actually a useful diagnostic tool that can help identify ignition problems before they leave you stranded. I dealt with this about two months ago with my truck. I'll say this, just because you replaced something doesn't mean the part you replaced it with was worth a chit. I initially replaced my coil and ICM and the issue persisted. Distributor was "new" some two years ago. Replaced the distributor with an O'Reilly's unit and my issue went away. You might also want to check your coil, they can cause flutter too. Two of the coils I got tested bad right in the box, I'm still running one I pulled from a treasure yard as a result.

 

[User_name]

That would make sense. I'm gonna go pick up a new coil and dizzy from orilleys and try that out.

 

[PlayingWithTBI]

If it's missing every time you see flutter, disconnecting the wire to the tach won't solve the issue. Not sure about a '95, but I'm confident that there are two tach signal wires, one for the ECM and one for the cluster.

^^^This as far as the tach but, I think the tach wire is the white one coming off the top of the coil.

 

[Schurkey]

It is possible for a tach failure to cause a misfire. NOT common.

It's far more likely that the tach is telling the truth--there's a misfire due to intermttent lack of ignition; and the tach is responding to the lack of RPM signal.

I'd kinda expect this to be a distributor problem (pickup coil or ignition module) or in the wire harness somewhere.

Connect a scan tool, look for interruptions in the RPM signal.

 

[User_name]

Another "theory" I have is this: could I have the wrong ignition module? I know that there are two different ones that are listed for my truck.
There are also 2 esc modules that are listed depending on the gvwr one is listed "under 8500 lbs" and another is "over 8500 lbs"
AFAIK it still has the original esc module. I was just wondering if the listing for the two different p/n ignition modules could also have that reasoning behind it. My truck is 8600 lb gvw. 8 lug.

 

[PlayingWithTBI]

There are also 2 esc modules that are listed depending on the gvwr one is listed "under 8500 lbs" and another is "over 8500 lbs"
AFAIK it still has the original esc module.

I'm not sure but, AFAIK 94s and 95s had the internal ESC module, the earlier TBIs had the external one.

 

[User_name]

@PlayingWithTBI my esc module is located on the intake, passenger side. You might be thinking of the vortecs?

 

[User_name]

Also, I noticed that my ecm is loose, someone before myself didn't fasten it back down. Could this be part of my issue? (Behind glovebox on mine) is it grounded through the body of the ecm in some way? I just remembered that..... I just can't seem to remember how they are held in the bracket.

 

[PlayingWithTBI]

I just can't seem to remember how they are held in the bracket.

The PCM sits on a shelf and is help by 2 clips where you slide the PCM towards the passenger side fender and the clips open a little to lock it in place.